Logic

For unless one has first come to the knowledge of what reasoning keeps the true path of disputing, what recognizes the probable, and which is trustworthy and which may be suspect, the uncorrupted truth of things cannot be found by reasoning. Since, therefore, the ancients, often falling into many errors, gathered in disputation certain false and self-contradictory conclusions, and it seemed impossible that, a contrary conclusion having been drawn on the same matter, both should be true which the reasoning had concluded against itself, and it was uncertain which reasoning should be believed, it seemed good first to consider the true and complete nature of disputation itself; this being known, it could also be understood whether what was found by disputation had been truly comprehended. From this, then, arose logic, the skill of the discipline which prepares the modes of disputing and the ways of discerning reasonings themselves, so that it may be recognized which reasoning is at one time true, at another false; which is always false, which never false. In time it is last, but in order first; for to those beginning philosophy it is to be read first, because in it is taught the nature of words and concepts, without which no treatise of philosophy can be reasonably unfolded.

All these operations are performed naturally, and oftentimes better by those who are unacquainted with the rules of logic than by those who know them.

Thus logic consists, not in discovering the means of performing these operations, since nature alone furnishes these in giving us reason, but in reflecting on that which nature does within us, which is of service to us in the following respects: —

First, In assuring us that we employ reason aright; for the consideration of the rule which guides it, awakens within us fresh attention to its operations.

Second, In enabling us to discover and explain more easily any error or defect which may be found in the operations of our mind; for it often happens that we discover, by the light of nature alone, that a reasoning is false, without being able to determine how it is so, as those who are not skilled in painting may be sensible of defect in a picture, without being able, nevertheless, to explain what is the blemish which offends them.

Third, In making us better acquainted with the nature of our mind, by the reflections which we thus make on its operations. And this is, in itself, more excellent, considered merely in a speculative point of view, than the knowledge of all corporeal things, which are infinitely beneath those which are spiritual.